Heretofore, the Kaminsky type catalysts containing a transition metal compound and aluminoxane have been known as a soluble olefin polymerization catalyst. For example, the following catalysts are known. In the alpha-olefin polymerization, a catalyst composed of a zirconium compound and aluminoxane shows high polymerization activity (Japanese Patent Application Unexamined Publication No. Sho 58-19309). Stereo-regular polypropylene is produced using a catalyst composed of a zirconium compound having a ligand in which two indenyl groups are connected through an ethylene group, and aluminoxane (JP Pat. Appln. Unexamined Pub. No. Sho 61-130314). It is said that using these Kaminsky type catalysts, for example in the propylene polymerization, any of isotactic polypropylene, atactic polypropylene and syndiotactic polypropylene can be produced (Macromol. Chem., Rapid Commun. 4,417-421 (1983); Angew. Chem. Int. Ed. Engl. 24,507-508 (1985); J. Am. Chem. Soc. 109,6544-6545 (1987); and J. Am. Chem. Soc. 110,6255-6256 (1988)).
In this case, as a transition metal compound useful for producing isotactic polypropylene, a transition metal compound having an ethylene bis(indenyl) ligand (JP Pat. Appln. Unexamined Pub. No. Sho 61-264010; Sho 64-51408; and Sho 64-66216); R(C.sub.5 (R').sub.4).sub.2 MeQp type metallocene compound reported by Ewen et al (JP Pat. Appln. Unexamined Pub. No. Sho 63-251405; Sho 63-295607; and Sho 64-74202); a metallocene compound cross-linked with silicon or the like (JP Pat. Appln. Unexamined Pub. No. Hei 3-12406); and the like are known. Further, a metallocene compound useful for producing a stereo-block polymer is known (JP Pat. Appln. Unexamined Pub. No. Sho 63-142004 and Sho 63-2005).
However, the above-mentioned polymerization methods require use of a great amount of expensive aluminoxane which is 100 to 10,000 times the amount of a transition metal compound to obtain sufficient activity. Further, due to use of a great amount of aluminoxane, a substantial amount of metal will remain in the polymerized products, resulting in deterioration and coloring of the products. In these processes, after polymerization, deashing treatment of the resultant products should be sufficiently conducted. Thus, these processes have a problem in productivity.
Further, aluminoxane is produced from the reaction of highly reactive trimethylaluminum and water, leading to risks. Furthermore, the reaction product is a mixture of several materials containing unreacted materials, and it is quite difficult to isolate one single substance. Thus, management of catalysts to obtain a product having stable physical properties is quite difficult.
On the other hand, JP Pat. Appln. PCT Pub. No. Hei 1-502036 discloses a polymerization process for producing an alpha-olefin polymer using, as a catalyst, a specific boron complex containing ammonium and a metallocene compound. However, the catalyst shows extremely low polymerization activity and thus is not suitable for industrial use.
Further, syndiotactic polyolefins, particularly syndiotactic polypropylene (SPP) are known. However, there are some problems in all conventional processes for producing syndiotactic polyolefins.
For example, it is known that SPP can be produced at -78.degree. C. using a catalyst system composed of VCl.sub.4, anisole and dibutylaluminum chloride (By B. Lotz et al, Macromolecules 21, 1988, 2375). However, the polymerization temperature is extremely low. Also, the stereo-regularity of the resultant product and the yield are extremely low.
Further, it is known that SPP can be obtained, at a drastically improved yield, at 25.degree. to 70.degree. C. using a catalyst composed of isopropylidene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride and methylaluminoxane (By J. A. Ewen et al., J. Am. Chem. Soc., 110, 1988, 6255). However, the SPP obtained in this process has low molecular weight.
Further, it is known that SPP having high molecular weight can be produced using [phenyl(methyl)methylene](9-fluorenyl)(cyclopentadienyl)zirconium dichloride or diphenylmethylene(9-fluorenyl)(cyclopentadienyl)zirconium dichloride, and methylaluminoxane (JP Pat. Appln. Unexamined Pub. No. Hei 2-274703). However, in this process, a great amount of expensive aluminoxane against a transition metal compound should be employed.
Accordingly, a process for producing syndiotactic polyolefin in an industrially effective way at high yield, has not yet been found.